Field of the Invention
The present invention relates generally to an internal combustion engine, and more specifically to an internal combustion engine with self-ignition.
Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
An internal combustion engine, such as one that powers an automobile, includes a combustion chamber with a reciprocating piston that compresses a gas and a spark plug that ignites the compressed gas a fuel mixture to produce combustion. A diesel engine does not make use of a spark plug, but uses the high pressure compressed air to auto-ignite a diesel fuel that is injected into the combustion chamber at near top-dead-center of the piston. A diesel engine cannot burn natural gas because the auto-ignition temperature of natural gas is much higher than the temperature produced in the gas from the compression. For this reason, a diesel engine would also inject a fuel such as diesel fuel into the compressed natural gas to ignite the compressed natural gas to produce combustion.
As pressures increase in an internal combustion engine to produce higher efficient engines, the temperature of the compressed gas also increases. Too high of a pressure results in to high of a temperature, and the compressed gas would ignite prematurely.
High thermal efficiency and reduced emissions, such as NOx, in a reciprocating internal combustion (IC) engine can be achieved by reducing the fuel/air ratio and increasing the break mean effective pressure. However, traditional ignition methods become unreliable as the mixture ratio becomes to lean, leading to higher coefficient of variation (COV) and spark plugs tend to fail via flash-over caused by the higher voltages required by the higher ignition pressure. These high voltages also reduce spark plug life due to higher erosion rates. As a result, elimination of the spark plug with a more reliable ignition method could improve emissions and enable efficiency gains to be realized with leaner mixtures and higher combustion pressures.
Also, spark plugs need to be replaced at regular intervals due to wear. This generally occurs during regularly scheduled maintenance, not necessarily when the spark plugs actually need to be replaced. When done this way, unforeseen shutdowns due to failures between scheduled maintenance intervals may occur. Therefore, eliminating the need for spark plugs will also reduce maintenance costs and engine down-time.
U.S. Pat. No. 4,969,425 issued to Slee on Nov. 13, 1990 and entitled PISTON WITH A RESONANT CAVITY discloses an internal combustion engine with a resonance cavity formed in the piston of to a side toward an exhaust port of the engine, and where the engine includes a spark plug to ignite the fuel and air mixture.